Dino
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Power Brakes

Tue Nov 30, 2010 5:49 pm

Does the Leaf have a vacuum pump for brake assist ?
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garygid
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Re: Power Brakes

Tue Nov 30, 2010 6:03 pm

These features are listed:

4-wheel Anti-lock Braking System (ABS)
Electronic Brake force Distribution (EBD)
Brake Assist (BA)

Chances are all of these, and any "Power Brake"
(it that the "Brake Assist"?) function, use the
hydraulic braking system to achieve their function.

Also, there is no source of vacuum on the EV.

So, I think a vacuum Power-Brake is unlikely.
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Smidge204
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Re: Power Brakes

Tue Nov 30, 2010 6:33 pm

My understanding is the Leaf is completely drive-by-wire, so there is no mechanical connection between any of the controls (steering, accelerator, brake, parking brake) and the actual mechanisms. So rather than a booster and master cylinder, it probably uses an electric hydraulic pump/ram of some kind.

There was some leaked info regarding maintenance a few weeks ago that mentions brake fluid flushes, so it's almost certainly hydraulic. The Service and Maintenance Guide (PDF) is a great flip-through and gives some nice details about the vehicle, like the fact that the HVAC system uses antifreeze coolant (Replace every 75,000 miles!)
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GroundLoop
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Re: Power Brakes

Tue Nov 30, 2010 6:50 pm

Smidge204 wrote:My understanding is the Leaf is completely drive-by-wire, so there is no mechanical connection between any of the controls (steering, accelerator, brake, parking brake) and the actual mechanisms. So rather than a booster and master cylinder, it probably uses an electric hydraulic pump/ram of some kind.
Wow, that would be a departure. I thought the US required direct mechanical steering and brakes on all cars. If this is the world's first steer-by-wire, well, I have think hard about whether I'm ready for that. :)

There's probably an electric brake pump that provides boost pressure, like a Prius.
Likewise, an electric steering pump for that overboosted steering feel.

Next time someone does a drive, try cranking the wheel over while the Leaf is off. I'd bet it feels pretty normal -- heavy, but mechanically connected.

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EVDRIVER
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Re: Power Brakes

Tue Nov 30, 2010 6:52 pm

The steering in normal and has electric assist, the P brake is an electric solenoid that pulls a cable. the brakes appear to be normal hydraulic electric-assisted, the accelerator is most likely a standard HEPI (Hall Effect Pedal Sensor), that's a magnetic sensor. There are e few hydraulic brake distribution blocks in the motor compartment.

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garygid
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Re: Power Brakes

Wed Dec 01, 2010 12:09 am

I believe the power steering's electric assist (to the normal mechanical steering) has no hydraulics involved (in the steering function). It could just be an electric motor coupled "directly" (through gears) to the steering shaft (and gear).
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wgs1912
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Re: Power Brakes

Wed Dec 01, 2010 11:05 am

Steering and brakes are both mechanically connected. Steering has an assist motor on steering column. The brakes have a motor mounted in a booster assembly. There is a stroke sensor in the booster assembly to read how fast and hard pedal is applied. From the video I watched at work it shows a "cooprative" brake system. It starts with mechanical brakes switches to regen then back to mechanical brakes at final stop.
Last edited by wgs1912 on Wed Dec 01, 2010 6:51 pm, edited 1 time in total.
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garygid
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Re: Power Brakes

Wed Dec 01, 2010 11:35 am

It applies the energy-wasting disc brakes BEFORE the Regen?

So, with a LONG Regen-Braking run you are (perhaps slowly) heating the brake pads to ... "very hot"?

Is that done so that the brake pads will already be touching (lightly) the brake rotors, ready for increased disc-braking pressure?
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EVDRIVER
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Re: Power Brakes

Wed Dec 01, 2010 11:42 am

garygid wrote:It applies the energy-wasting disc brakes BEFORE the Regen?

So, with a LONG Regen-Braking run you are (perhaps slowly) heating the brake pads to ... "very hot"?

Is that done so that the brake pads will already be touching (lightly) the brake rotors, ready for increased disc-braking pressure?

Classic example of poor regen to make the car "normal" The brakes wont drag on ECO.

Smidge204
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Re: Power Brakes

Wed Dec 01, 2010 12:01 pm

GroundLoop wrote:Wow, that would be a departure. I thought the US required direct mechanical steering and brakes on all cars. If this is the world's first steer-by-wire, well, I have think hard about whether I'm ready for that. :)

There's probably an electric brake pump that provides boost pressure, like a Prius.
Likewise, an electric steering pump for that overboosted steering feel.

Next time someone does a drive, try cranking the wheel over while the Leaf is off. I'd bet it feels pretty normal -- heavy, but mechanically connected.
Pretty much my position on it. I know drive-by-wire cars exist as prototype/concept vehicles, and that drive-by-wire systems are common on industrial equipment (construction vehicles, forklifts, etc). But I just had the impression that the Leaf was also drive-by-wire. I'd be a little :| about that.

But from what others have said it seems I was mistaken about that, which is good IMHO! Part of what convinced me of this was the electrically operated parking brake instead of a normal cable pull arrangement. (I wonder if that has anything to do with the battery pack taking up the entire underchassis?)

wgs1912 wrote:From the video I watched at work it shows a "cooprative" brake system. It starts with mechanical brakes switches to regen then bake to mechanical brakes at final stop.

I would love to see the video you're referring to. That just seems like unnecessary wear on the brakes.
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